Field demonstration of the combined use of thermally-degrading and cation-exchanging tracers to predict thermal drawdown in a geothermal reservoir

A tracer test was conducted in a geothermal reservoir using a cation-exchanging tracer to interrogate flow pathway surface area to volume ratios and a thermally-degrading tracer to interrogate average flow pathway temperatures. The test interpretations are used to predict when thermal drawdown will occur at a production well due to injecting cooler spent geothermal water into an injection well. The cation-exchanging tracer provides constraints on the timing of thermal drawdown, and the thermally-degrading tracer provides constraints on the magnitude of thermal drawdown. Uncertainties associated with the method, including assumptions made about flow pathway geometry, are discussed.